A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
Sulfur dioxide, organic phosphates, amines, and oxygen are contaminants typically found in a lithographic apparatus that may decrease the yield of good dies by attaching to the substrates, to the projection system of the lithographic apparatus, or to other sensitive parts of the lithographic apparatus. While the internal and external ambient atmosphere of the lithographic apparatus is typically controlled to reduce the levels of such contaminants, there is however invariably some level of contamination of sensitive parts of the lithographic apparatus or contamination of materials supplied to the lithographic apparatus. For example, contaminants may be introduced into the ambient atmosphere via an incoming substrate, outgassing of materials, leakage of contaminated gas into the lithographic apparatus, maintenance of the lithographic apparatus by personnel, etc.